In power semiconductor devices a blocking voltage applied between a first load electrode at a front side and a second load electrode on the back of a semiconductor the forms a depletion zone along a main pn junction. Since along a lateral outer surface the blocking capability of the semiconductor die is low, the main pn junction is typically designed such that the depletion zone extends from a central doped zone into the lateral direction and such that the lateral outer surface remains free of electric fields. As a consequence, lateral and vertical components of an electric field between the first and second load electrodes may superimpose along a curved section of the blocking main pn junction. Lateral junction termination extensions with gradually decreasing dopant concentration expand a central doped zone along a surface of the semiconductor die at the front side, flatten the curved section of the main pn junction, and improve the blocking capability. In semiconductor materials in which dopants have a sufficient diffusion length, lateral junction termination extensions of the central doped zone form a gradual transition between the central doped zone and the surrounding edge region by diffusion of dopants implanted through a small number of implants using different implant masks. In semiconductor devices based on materials, in which diffusion length of the dopants is low, a high number of implants with different implant masks may form a junction termination extension in which the dopant concentration varies with sufficient smoothness. Alternatively, one single implant may use an implant mask with openings which diameters decrease with decreasing distance to the edge region or one single implant may use a wedge-shaped implant mask to form graded junction termination extensions.
There may be a need to simplify formation of doped zones with laterally varying concentration of dopants in semiconductor materials in which a diffusion length of dopants is low.